**2.2 Result**

The coupled calculations were verified using measured data from an actual room air conditioner in heating operation. The heat exchanger has six paths upstream of the refrigerant circuit, four paths in the midstream using a distributor, and two paths further downstream.

**Table 2** is comparison of experimental and numerical data of air-side CFD model. Air flow volume rate is from the air-side CFD (airflow) result and heat capacity value is from the air-side CFD (heat conductivity). Amount of heat capacity of CFD is 4% larger than experimental.

**Figure 8a** and **b** show the air-side CFD (heat conductivity) result at the third run. **Figure 8a** is the airflow velocity contour plot, and **Figure 8b** is the airflow temperature contour plot. The value of the airflow velocity entering the heat exchanger is between 3.0 (m/s) and 4.0 (m/s) at the most area. There are areas where the airflow velocity is lower than 1.0 (m/s), such as at the front bended area and at the part of back of the heat exchanger. Previous research papers [3, 4] assume that the direction of airflow enters vertically into the front of the heat exchanger and direction are not changed, but calculation result shows airflow enter the front of the heat exchanger at various angles and that the direction changes inside the fins.

The air temperature distribution can be roughly classified into three areas. The area with a temperature near 20 °C is the airflow flowing into the inlet of the indoor unit.

*Application of CFD to Prediction of Heat Exchanger Temperature and Indoor Airflow Control… DOI: http://dx.doi.org/10.5772/intechopen.110076*

**Figure 8.** *Result of air-side CFD calculation: (a) airflow velocity contour plot; (b) airflow temperature contour plot.*

Since the temperature of the refrigerant state is 20 °C in the liquid phase, the temperature of the airflow passing through the tubes at the top of the heat exchanger, which is in the liquid phase, is around 20 °C. The temperature of the refrigerant state in the twophase flow is approximately 40 °C. The temperature of the airflow passing through the tubes in the two-phase flow section rises as it exchanges heat with the refrigerant. The tubes of the downwind side of the heat exchanger flow refrigerant vapor phase state, and the temperature of the pipes in the vapor phase exceeds 45 °C. The temperature of the airflow passing through these tubes is above 45 °C.

**Figure 9** shows the fin surface temperature, focusing on the part of the fin where conductivity occurs between the vapor phase flow tubes (high temperature) and vapor/liquid phase tube (low temperature). A role of a heat exchanger is a heat exchange function between air and refrigerant. If the temperature difference in the refrigerant piping is large, heat exchange occurs between the refrigerant tubes. In this case, some tubes do not contribute to improved heat capacity, which is called "fin conductivity [4]." These models use fine fin mesh and can calculate heat transfer *via* fins.

**Figure 10** shows the result of the refrigeration circuit model calculation using pressure and enthalpy plotted for node elements (p-h diagram). The refrigeration circuit consists of 12 paths. There are two refrigerant inlets, a distributor device, and four outlets. In the heating mode, the enthalpy of refrigerant flow decreases from the refrigerant flow inlet to the outlet because of heat transfer between the refrigerant and

**Figure 9.** *Fin conductivity: (a) CFD result of fin surface temperature and (b) schematic illustration*.

#### **Figure 10.**

*A p-h diagram of refrigerant flow in the heat exchanger for each of 12 paths. Dots represent pressure and enthalpy values of node elements of tubes. Each path consists of 6 to 8 tubes. The distributor divides these paths into upstream side and downstream side. Paths 1 through 6 are upstream paths, and paths 11 through 12 are downstream paths.*

the airflow. This result shows that our numerical model can quantify the energy loss due to fin conductivity.
